The problem is that there are tricks which allow you to determine what is in them. So it's not so much about buying much more valuable stuff but the risk of players tricking others to buy one while they know it's pretty much useless.

These chests are best used (opened) or stored in a collection. Or given away of course.

Selling the Bonus Chest for the container and not the items looks good on paper, but it's actually really impractical and wouldn't work at all. Players would be saying "I'm buying for the chest only" but they really wouldn't be. In the back of their mind they'd want something good. There's no way to guarantee someone would be buying the chest for just the container.

Even if players agree to the risks of selling, it doesn't prevent scamming, and scamming is very, very easy for Bonus Chests. There are ways to tell exactly what's in a bonus chest before they're opened. Again, things like "I'm pretty sure this contains a diamond voucher" when it really contains obsidian are great reasons why they shouldn't be sold.

Selling the Bonus Chest for the container and not the items looks good on paper, but it's actually really impractical and wouldn't work at all. Players would be saying "I'm buying for the chest only" but they really wouldn't be. In the pack of their mind they'd want something good. There's no way to guarantee someone would be buying the chest for just the container.

Even if players agree to the risks of selling, it doesn't prevent scamming, and scamming is very, very easy for Bonus Chests. There are ways to tell exactly what's in a bonus chest before they're opened. Again, things like "I'm pretty sure this contains a diamond voucher" when it really contains obsidian are great reasons why they shouldn't be sold.